Never ever again! I am SO HAPPY for you you changed your dates!
The first year we lived in Florida (2005) my brother, Mom and Dad flew in . . . long weekend . . . we went the Thurs-Mon and OMG!! The heat, the people, the heat THE HEAT!
It was so crowded they CLOSED MK at 12 noon! They would only let people in as people left . . . 3 left, 3 got in!! I swear it was that much hotter cuz the park was at capacity!
The fireworks at nite are to die for . . . but other then that avoid it at all costs!!
But that's not to say, you couldn't do other things . . . like TREAT DW to a lushish spa treatment at the GF!!
or just sit and relax by the pool!
Sometimes a good WDW world vacation doesn't even include the theme parks!!
PS. I went last year too end of July, which wasn't as bad as 4th of July, but I won't go again in July. When you are spoiled with going during the "off season" it's VERY hard to go during peak and in the heat!!